The invention relates to a threaded bolt assembly to be anchored in a drilled hole having an undercut and formed in a concrete part, with a hardening compound mass.
Anchoring of a threaded bolt assembly in a drilled hole with a hardening compound mass is disclosed in DE-0S 35 16 866. In the DE-OS 35 16 866, the threaded bolt has, at its leading end face a tapered enlargment, the largest external diameter of which is somewhat smaller than the diameter of the drilled hole for insertion through the cylindrical part of the drilled hole. Thus, the anchoring effect of this threaded bolt is based exclusively on the shear action of the hardened compound mass. In uncracked concrete, this shear action is sufficient to achieve high fixing values, but when such an anchorage is effected in the tension zone of a concrete part, where cracks running through the fixing point may occur as a result of tensile stresses after the fixing elements have been anchored, the compound mass becomes detached from the wall of the drilled hole. A threaded bolt set in a purely cylindrical drilled hole is therefore unable to accommodate any further holding forces. In the case of the threaded bolt according to the DE-OS 35 16 866, the same effect is admittedly produced for the anchorage in the region of the cylindrical part of the drilled hole. However, in the region of the undercut, a matching fit is obtained, which prevents a total failure of the holding force. Certainly the holding force is based exclusively on the shear strength of the compound mass in the region of the undercut, but the latter is considerably less than the resistance to fracture of the concrete.